# How to capture a for loop index after break?
**URL:** https://discourse.julialang.org/t/how-to-capture-a-for-loop-index-after-break/46342
**Category:** General Usage
**Created:** [September 9, 2020, 6:56pm UTC](https://discourse.julialang.org/t/how-to-capture-a-for-loop-index-after-break/46342 "2020-09-09T18:56:10Z")
**Posts on this page:** 20
**Page:** 1
### Author:  [@pauljurczak](https://discourse.julialang.org/u/pauljurczak)
#### Post date: [September 9, 2020, 6:56pm UTC](https://discourse.julialang.org/t/how-to-capture-a-for-loop-index-after-break/46342/1 "2020-09-09T18:56:10Z")
Is there a way to have a non-local scope loop index, so code similar to this:
```julia
for i = 1:9
if i > 3
break
end
end
println(i)
```
works and I don’t have to write:
```julia
j = 0
for i = 1:9
if i > 3
j = i
break
end
end
println(j)
```
---
### Author:  [@jling](https://discourse.julialang.org/u/jling)
#### Post date: [September 9, 2020, 7:18pm UTC](https://discourse.julialang.org/t/how-to-capture-a-for-loop-index-after-break/46342/2 "2020-09-09T19:18:23Z")
no easy / canonical way because `for...end` forms a local scope, there’s this hack:
```julia
julia> j = Ref(-1)
Base.RefValue{Int64}(-1)
julia> for j[] = 1:10
if j[]>3
break
end
end
julia> j[]
4
```
But I’d recommend against it.
---
### Author:  [@pauljurczak](https://discourse.julialang.org/u/pauljurczak)
#### Post date: [September 9, 2020, 7:25pm UTC](https://discourse.julialang.org/t/how-to-capture-a-for-loop-index-after-break/46342/3 "2020-09-09T19:25:40Z")
Was `for global i = 1:9` syntax ever proposed?
---
### Author:  [@jebej](https://discourse.julialang.org/u/jebej)
#### Post date: [September 9, 2020, 7:27pm UTC](https://discourse.julialang.org/t/how-to-capture-a-for-loop-index-after-break/46342/4 "2020-09-09T19:27:53Z")
Are you looking for the `outer` keyword?
```julia
function foo(p)
local i
for outer i = 1:100
rand() > p && break
end
return i
end
```
---
### Author:  [@jling](https://discourse.julialang.org/u/jling)
#### Post date: [September 9, 2020, 7:30pm UTC](https://discourse.julialang.org/t/how-to-capture-a-for-loop-index-after-break/46342/5 "2020-09-09T19:30:33Z")
😮 , first time seeing this anywhere and `?outer` has nothing to offer, neither do `for`’s manual page or docs. Btw you don’t need the first `local` I think.
---
### Author:  [@pauljurczak](https://discourse.julialang.org/u/pauljurczak)
#### Post date: [September 9, 2020, 7:31pm UTC](https://discourse.julialang.org/t/how-to-capture-a-for-loop-index-after-break/46342/6 "2020-09-09T19:31:41Z")
Same here. Really hard to find.
---
### Author:  [@jebej](https://discourse.julialang.org/u/jebej)
#### Post date: [September 9, 2020, 7:32pm UTC](https://discourse.julialang.org/t/how-to-capture-a-for-loop-index-after-break/46342/7 "2020-09-09T19:32:20Z")
It does seem hard to find. The documentation mentions this feature here:
[https://docs.julialang.org/en/v1/manual/variables-and-scoping/#Loops-and-Comprehensions](https://docs.julialang.org/en/v1/manual/variables-and-scoping/#Loops-and-Comprehensions)
---
### Author:  [@pauljurczak](https://discourse.julialang.org/u/pauljurczak)
#### Post date: [September 9, 2020, 7:34pm UTC](https://discourse.julialang.org/t/how-to-capture-a-for-loop-index-after-break/46342/8 "2020-09-09T19:34:05Z")
> [@jling](#):
>
> Btw you don’t need the first `local`
True. This works fine:
```julia
function foo(p)
i = 0
for outer i = 1:100
rand() > p && break
end
return i
end
```
---
### Author:  [@jebej](https://discourse.julialang.org/u/jebej)
#### Post date: [September 9, 2020, 7:42pm UTC](https://discourse.julialang.org/t/how-to-capture-a-for-loop-index-after-break/46342/9 "2020-09-09T19:42:40Z")
> [@jling](#):
>
> Btw you don’t need the first `local` I think.
You just need the variable to exist in the outer scope. Using `local` is the least constraining way of doing that.
For example if you decide later to change the type of the loop variable (e.g. to `for i = 1.0 : 10.0`), having `i=0` hardcoded will lead to a type instability. With local, `i` will always have the right type.
Another advantage is that you can reliably check whether the loop ran at all:
```julia
julia> function testfun(p)
local i
for i = 1:100
rand() > p && break
end
if @isdefined(i)
return i
else
return 999
end
end
testfun (generic function with 1 method)
julia> testfun(0.99)
999
```
---
### Author:  [@baggepinnen](https://discourse.julialang.org/u/baggepinnen)
#### Post date: [September 9, 2020, 7:50pm UTC](https://discourse.julialang.org/t/how-to-capture-a-for-loop-index-after-break/46342/10 "2020-09-09T19:50:41Z")
In this case it would be easier to just return I from the loop?
---
### Author:  [@pauljurczak](https://discourse.julialang.org/u/pauljurczak)
#### Post date: [September 9, 2020, 8:09pm UTC](https://discourse.julialang.org/t/how-to-capture-a-for-loop-index-after-break/46342/11 "2020-09-09T20:09:55Z")
> [@baggepinnen](#):
>
> return I from the loop
You mean return `i`, right? My actual use case is more complex and I can’t do it, but in the `foo` example above, it is definitely an option.
---
### Author:  [@pauljurczak](https://discourse.julialang.org/u/pauljurczak)
#### Post date: [September 9, 2020, 8:42pm UTC](https://discourse.julialang.org/t/how-to-capture-a-for-loop-index-after-break/46342/12 "2020-09-09T20:42:27Z")
> [@jebej](#):
>
> you can reliably check whether the loop ran at all
In this case I would rather write:
```julia
function testfun(p)
i = 999
for outer i = 1:100
rand() > p && break
end
return i
end
```
but I see where `local` may be useful.
---
### Author:  [@pauljurczak](https://discourse.julialang.org/u/pauljurczak)
#### Post date: [September 10, 2020, 2:05pm UTC](https://discourse.julialang.org/t/how-to-capture-a-for-loop-index-after-break/46342/13 "2020-09-10T14:05:52Z")
BTW, `outer` is not recognized as a keyword by Discourse.
---
### Author:  [@simeonschaub](https://discourse.julialang.org/u/simeonschaub)
#### Post date: [September 10, 2020, 4:12pm UTC](https://discourse.julialang.org/t/how-to-capture-a-for-loop-index-after-break/46342/14 "2020-09-10T16:12:18Z")
That’s because it’s not actually a reserved keyword, `outer` only has special meaning in the iteration specification of for loops and generators. That’s why the following are still completely valid syntax:
```julia
julia> outer = 7
7
julia> for outer in 1:3
println(outer)
end
1
2
3
julia> for outer * inner ∈ 1:3
println(1 * 2)
end
1
2
3
```
---
### Author:  [@pauljurczak](https://discourse.julialang.org/u/pauljurczak)
#### Post date: [September 10, 2020, 4:19pm UTC](https://discourse.julialang.org/t/how-to-capture-a-for-loop-index-after-break/46342/15 "2020-09-10T16:19:04Z")
Hmm, that looks quite a bit error-prone.
---
### Author:  [@simeonschaub](https://discourse.julialang.org/u/simeonschaub)
#### Post date: [September 10, 2020, 5:51pm UTC](https://discourse.julialang.org/t/how-to-capture-a-for-loop-index-after-break/46342/16 "2020-09-10T17:51:57Z")
Why is that error prone? It would be pretty annoying not being able to name variables `outer` in normal code anymore, just for this special for loop syntax.
---
### Author:  [@tkf](https://discourse.julialang.org/u/tkf)
#### Post date: [September 10, 2020, 6:07pm UTC](https://discourse.julialang.org/t/how-to-capture-a-for-loop-index-after-break/46342/17 "2020-09-10T18:07:28Z")
(I had no idea what `for outer * inner ∈ 1:3` does and I had to stare at `Meta.@lower` output for a while. This is so diabolical and I love this example 🤣)
---
### Author:  [@pauljurczak](https://discourse.julialang.org/u/pauljurczak)
#### Post date: [September 10, 2020, 7:13pm UTC](https://discourse.julialang.org/t/how-to-capture-a-for-loop-index-after-break/46342/18 "2020-09-10T19:13:18Z")
> [@simeonschaub](#):
>
> Why is that error prone
OK, maybe not error-prone, since compiler will help here, but context sensitive behavior of `outer` may be a bit confusing. I don’t think identifiers, which may or may not be restricted keywords depending on context, are widely used in programming languages. Maybe I’m too old date…
---
### Author:  [@pauljurczak](https://discourse.julialang.org/u/pauljurczak)
#### Post date: [September 10, 2020, 7:21pm UTC](https://discourse.julialang.org/t/how-to-capture-a-for-loop-index-after-break/46342/19 "2020-09-10T19:21:29Z")
> [@tkf](#):
>
> This is so diabolical
Way too diabolical for me! Can you explain what is happening there? Why are we getting anything other than `2` as in:
```julia
julia> println(1 * 2)
2
```
---
### Author:  [@tkf](https://discourse.julialang.org/u/tkf)
#### Post date: [September 10, 2020, 8:53pm UTC](https://discourse.julialang.org/t/how-to-capture-a-for-loop-index-after-break/46342/20 "2020-09-10T20:53:00Z")
I don’t want spoil anyone’s fun so I’m hiding the explanation behind `[spoiler]` (click to remove the blur):
```julia
for outer * inner ∈ 1:3
println(1 * 2)
end
```
behaves as above since it is equivalent to
```julia
for x ∈ 1:3
_ * _ = x
println(:this_is_ignored * :this_is_also_ignored)
end
```
(Note also that `_ * _ = x` is equivalent to `*(_, _) = x`; i.e., it defines a closure named `*`.)
Perhaps the best way to see what is going on is to print what `*` is:
```julia
julia> for outer * inner ∈ 1:3
@show *
println(:ignored * :ignored)
end
* = var"#*#12"{Int64}(1)
1
* = var"#*#12"{Int64}(2)
2
* = var"#*#12"{Int64}(3)
3
```
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